AFAICT at least 2 people in this thread don't seem to think that visibility -- a function of, among other things, weather and time of day -- influences driving safety. I find this amazing.
The point of terryf's example was to point out that for practical reasons, existing laws don't capture every relevant variable. I (but not everyone, it seems) think that visibility obviously influences safety. The point I want to make is that in practice the "precision gap" can't be perfectly rectified by making legality a function of more factors than just speed. There will always be some additional factor that influences the probability of a crash by some small amount -- and some of the largest factors, like individual driving ability, would be objected to on other grounds.
The point of terryf's example was to point out that for practical reasons, existing laws don't capture every relevant variable. I (but not everyone, it seems) think that visibility obviously influences safety. The point I want to make is that in practice the "precision gap" can't be perfectly rectified by making legality a function of more factors than just speed. There will always be some additional factor that influences the probability of a crash by some small amount -- and some of the largest factors, like individual driving ability, would be objected to on other grounds.